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- ID:
- ivo://CDS.VizieR/J/ApJ/858/71
- Title:
- CHARA array obs. of 13 AB Dor moving group stars
- Short Name:
- J/ApJ/858/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric measurements obtained with the CHARA Array of 13 adolescent-age stars in nearby moving groups. The motivation was to spatially resolve the largest stars and to search for binary companions. Nine stars have diameters smaller than the resolution limit and no evidence for companions within 0.5-50mas and {Delta}H<2.0mag. The diameters of three stars were spatially resolved: GJ 159 (0.582+/-0.016mas) and GJ 393 (0.564+/-0.021mas) in the AB Dor moving group, and former member HD 89744 (0.556+/-0.032mas). Combining the angular diameters with their distances and bolometric fluxes, we measured radii and effective temperatures. The temperatures of GJ 159 (6286+/-123K) and GJ 393 (3515+/-68K) are consistent with spectroscopic measurements. Comparisons with evolutionary models show that HD 89744 has evolved off the main sequence. GJ 159 and GJ 393 lie within 1.5{sigma} of the zero-age main sequence, complicating their age estimates because it is unclear whether the stars are contracting or expanding. GJ 159 has a mass of 1.2+/-0.1M_{sun}_ with an age spanning 0.021-3.0Gyr. Its debris disk and lithium abundance favor a young age. GJ 393 has a mass of 0.42+/-0.03M_{sun}_ and a lower limit on its age 0.06Gyr. This overlaps with the age of the moving group; however, an older age would be more consistent with its slow rotation, low activity, and luminosity, suggesting that GJ 393 is a kinematic interloper.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1556
- Title:
- Characterization of dusty debris disks
- Short Name:
- J/ApJ/660/1556
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dusty debris disks around main-sequence stars are signposts for the existence of planetesimals and exoplanets. From cross-correlating Hipparcos stars with the IRAS catalogs, we identify 146 stars within 120pc of Earth that show excess emission at 60um. This search took special precautions to avoid false positives. Our sample is reasonably well distributed from late B to early K-type stars, but it contains very few later type stars. Even though IRAS flew more than 20 years ago and many astronomers have cross-correlated its catalogs with stellar catalogs, we were still able to newly identify debris disks at as many as 33 main-sequence stars; of these, 32 are within 100pc of Earth. The power of an all-sky survey satellite like IRAS is evident when comparing our 33 new debris disks with the total of only 22 dusty debris disk stars first detected with the more sensitive, but pointed, satellite ISO. Our investigation focuses on the mass, dimensions, and evolution of dusty debris disks.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A88
- Title:
- Chemistry in infrared dark clouds
- Short Name:
- J/A+A/527/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars play an important role in shaping the structure of galaxies. Infrared dark clouds (IRDCs), with their low temperatures and high densities, have been identified as the potential birthplaces of massive stars. In order to understand the formation processes of massive stars, the physical and chemical conditions in infrared dark clouds have to be characterized. The goal of this paper is to investigate the chemical composition of a sample of southern infrared dark clouds. One important aspect of the observations is to check, whether the molecular abundances in IRDCs are similar to the low-mass pre-stellar cores, or if they show signatures of more evolved evolutionary stages. We performed observations toward 15 IRDCs in the frequency range between 86 and 93GHz using the 22-m Mopra radio telescope. In total, 13 molecular species comprising N_2_H^+^, ^13^CS, CH_3_CN, HC_3_N, HNC, HCO^+^, HCN, HNCO, C_2_H, SiO, H^13^CO^+^, H^13^CN, and CH_3_C_2_H were observed for all targets. Hence, we included in general species appropriate for elevated densities, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes.
- ID:
- ivo://CDS.VizieR/J/other/RAA/10.67
- Title:
- CH_3_OH maser sources
- Short Name:
- J/other/RAA/10.6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the 13.7m telescope of the Purple Mountain Observatory (PMO), a survey of the J=1-0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/105
- Title:
- [CII], [OI] and [OIII] line emission from z~6 gal.
- Short Name:
- J/ApJ/846/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Of the almost 40 star-forming galaxies at z>~5 (not counting quasi-stellar objects) observed in [CII] to date, nearly half are either very faint in [CII] or not detected at all, and fall well below expectations based on locally derived relations between star formation rate and [CII] luminosity. This has raised questions as to how reliable [CII] is as a tracer of star formation activity at these epochs and how factors such as metallicity might affect the [CII] emission. Combining cosmological zoom simulations of galaxies with SIGAME (SImulator of GAlaxy Millimeter/submillimeter Emission), we modeled the multiphased interstellar medium (ISM) and its emission in [CII], as well as in [OI] and [OIII], from 30 main-sequence galaxies at z~6 with star formation rates ~3-23M_{sun}_/yr, stellar masses ~(0.7-8)x10^9^M_{sun}_, and metallicities ~(0.1-0.4)xZ_{sun}_. The simulations are able to reproduce the aforementioned [CII] faintness of some normal star-forming galaxy sources at z>=5. In terms of [OI] and [OIII], very few observations are available at z>~5, but our simulations match two of the three existing z>~5 detections of [OIII] and are furthermore roughly consistent with the [OI] and [OIII] luminosity relations with star formation rate observed for local starburst galaxies. We find that the [CII] emission is dominated by the diffuse ionized gas phase and molecular clouds, which on average contribute ~66% and ~27%, respectively. The molecular gas, which constitutes only ~10% of the total gas mass, is thus a more efficient emitter of [CII] than the ionized gas, which makes up ~85% of the total gas mass. A principal component analysis shows that the [CII] luminosity correlates with the star formation activity of a galaxy as well as its average metallicity. The low metallicities of our simulations together with their low molecular gas mass fractions can account for their [CII] faintness, and we suggest that these factors may also be responsible for the [CII]-faint normal galaxies observed at these early epochs.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/68
- Title:
- [CII]157.7um feature in LIRGs
- Short Name:
- J/ApJ/774/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a survey of the [CII]157.7{mu}m emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky LIRG Survey (GOALS) sample, obtained with the PACS instrument on board the Herschel Space Observatory. The [CII] luminosities, L_[CII]_, of the LIRGs in GOALS range from ~10^7^ to 2x10^9^L_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/616/707
- Title:
- Circumnuclear structure of NICMOS galaxies
- Short Name:
- J/ApJ/616/707
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Why are the nuclei of some galaxies more active than others? If most galaxies harbor a central massive black hole, the main difference is probably in how well it is fueled by its surroundings. We investigate the hypothesis that such a difference can be seen in the detailed circumnuclear morphologies of galaxies using several quantitatively defined features, including bars, isophotal twists, boxy and disky isophotes, and strong nonaxisymmetric features in unsharp-masked images. These diagnostics are applied to 250 high-resolution images of galaxy centers obtained in the near-infrared with NICMOS on the Hubble Space Telescope. To guard against the influence of possible biases and selection effects, we have carefully matched samples of Seyfert 1, Seyfert 2, LINER, starburst, and normal galaxies in their basic properties, taking particular care to ensure that each was observed with a similar average scale (10-15pc/pixel).
- ID:
- ivo://CDS.VizieR/J/A+A/642/A86
- Title:
- Circumstellar disks in Lupus complex
- Short Name:
- J/A+A/642/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous star formation studies have, out of necessity, often defined a population of young stars confined to the proximity of a molecular cloud. Gaia allows us to examine a wider, three-dimensional structure of nearby star forming regions, leading to a new understanding of their history. We present a wide-area survey covering 494 deg^2^ of the Lupus complex, a prototypical low-mass star forming region. Our survey includes all known molecular clouds in this region as well as parts of the Upper Scorpius and Upper Centaurus Lupus (UCL) groups of the Sco-Cen complex. We combine Gaia DR2 proper motions and parallaxes as well as ALLWISE mid-infrared photometry to select young stellar objects (YSOs) with disks. The YSO ages are inferred from Gaia color-magnitude diagrams, and their evolutionary stages from the slope of the spectral energy distributions. We find 98 new disk-bearing sources. Our new sample includes objects with ages ranging from 1 to 15Myr and masses ranging from 0.05 to 0.5M_{sun}_, and consists of 56 sources with thick disks and 42 sources with anemic disks. While the youngest members are concentrated in the clouds and at distances of 160 pc, there is a distributed population of slightly older stars that overlap in proper motion, spatial distribution, distance, and age with the Lupus and UCL groups. The spatial and kinematic properties of the new disk-bearing YSOs indicate that Lupus and UCL are not distinct groups. Our new sample comprises some of the nearest disks to Earth at these ages, and thus provides an important target for follow-up studies of disks and accretion in very low mass stars, for example with ALMA and ESO-VLT X-shooter.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/67
- Title:
- Circumstellar emission measures with Keck
- Short Name:
- J/ApJ/734/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main-sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1-4AU from the star. We find one significant detection ({eta} Crv), two marginal detections ({gamma} Oph and {alpha} Aql), and 22 clear non-detections. Using a model of our own solar system's zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are {eta} Crv (1250+/-260), {gamma} Oph (200+/-80), and {alpha} Aql (600+/-200), where the uncertainties are 1{sigma}. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1{sigma}). These measurements represent the best limits to date on exozodi levels for a sample of nearby main-sequence stars. A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding {eta} Crv and {gamma} Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3{sigma} upper limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.
